Make one with each reindeer's name:
Dasher - Loves to run to keep cold, all day and all night long (Refrigerator)
Dancer - Dances when he has to go to this room (bathroom)
Prancer - Prancing around here may get you hurt (staircase)
Vixen - Lots of girls want to be vixen, find them here (computer)
Comet - Comet can fly and so can Aladdin when he uses this (carpet or rug of some sort, maybe under her bed if you have no rugs)
Cupid - Only cupid could bring this much love (find a picture on a mantle or something)
Donner - Don we now our gay apparel (some other Christmas decoration around your house)
Blitzen - You get blitzed with cold when you go here in the winter (windowsill)
Rudolph - This lights up just like his nose (Christmas tree!)
That sounds like a great fun thing to do, your sister will love it and what an awesome brother!! Merry Christmas!